This section provides background information related to the present disclosure which is not necessarily prior art.
Internal combustion engines may output undesirable pollution emissions, specifically in the form of oxides of nitrogen (NOx). One method used to reduce NOx emissions from internal combustion engines is known as selective catalytic reduction (SCR). SCR, when used, for example, to reduce NOx emissions from a diesel engine, involves injecting an atomized reagent into the exhaust stream of the engine in relation to one or more selected engine operational parameters, such as exhaust gas temperature, engine rpm or engine load as measured by engine fuel flow, turbo boost pressure or exhaust NOx mass flow. The reagent/exhaust gas mixture is passed through a reactor containing a catalyst, such as, for example, activated carbon, or metals, such as platinum, vanadium or tungsten, which are capable of reducing the NOx concentration in the presence of the reagent.
A diesel emissions fluid such as an aqueous urea solution is known to be an effective reagent in SCR systems for diesel engines. Use of such an aqueous urea solution, however, and other reagents may include disadvantages. Aqueous urea has a freezing point of approximately −11° C. In some climates, the aqueous urea will freeze to a solid state. One or more heaters may need to be employed to assure proper operation of the exhaust treatment system.
In at least one known arrangement, a flange style heating unit is positioned within the reagent tank. A central volume or core of liquid reagent is obtained by thawing the frozen reagent. During some modes of operation, the liquid reagent may be completely consumed and pumped from the tank prior to melting the remaining frozen reagent. Pump cavitation may occur. Pump damage may result. Furthermore, reagent will not be pumped into the exhaust stream and the vehicle may fail emissions testing. Pumping of the liquid reagent from a cavity adjacent the heating element may form a substantial vacuum within the vacated cavity. Damage to the pump or other exhaust treatment system components may result. As such, it may be advantageous to provide an improved reagent injection system to address these concerns.